Two micrograms per kilogram LSD-25 was administered intravenously to five normal subjects. The concentration of drug in plasma was determined serially over the subsequent 8 hours. LSD-25 was found to be present in human plasma in relatively large quantities during the period of peak effect. The half-life of LSD-25 in human plasma was calculated of be 175 minutes.

Five normal male subjects ages 21 to 25, were administered LSD-25 intravenously over a 1.5 minute period. Each subject received a dose equivalent to 2 mcg. per kilogram of the free base (given in the form of the tartrate salt). Blood samples drawn at 5, 15, 30, 60, 120, 240, and 480 minutes were heparinized and centri fuged. The plasma was separated, frozen, and later analyzed for LSD-25 with a slight modification of the method of Axelrod and co-workers.1

Since the quantities of LSD-25 to be measured at the dose used were relatively small, all glassware and equipment concerned with the analysis were scrupulously cleaned with nonfluorescent soap (Drene), rinsed, and then washed five times with distilled water. Pipettes were rinsed twice with the appropriate reagent before use. Five milliliters of plasma placed in a 40 ml. glass tube was salt saturated, alkalinized with 0.25 ml. 2N NaOH, and gently extracted for 30 minutes with 20 ml. of fluorescent grade n-heptane (Harleco), containing 2 per cent isoamyl alcohol, with the use of an Extractomatic shaker (Virtis). It was found that more violent agitation caused elevation of control readings. After extraction and eentrifugation, 18 ml. of the heptane layer was placed in a tube containing 1 ml. of 0.004 N HC1, and acid-heptane mixture was shaken (Extractomatic) for 15 minutes.

The heptane supernatant was removed and the 1 ml. acid phase was placed into a 1.4 ml. quartz cuvette. Fluorescence of the solution was measured with an Aminco-Bowman spectrophotofluorometer. Excitation and fluorescent wavelengths were 325 and 445 mu, respectively.

Internal standards with pretest plasma drawn just prior to the experiment were carried through the analysis. The internal standards contained 0, 10, 20, and 40 ng. of added LSD-25. The sensitivity of the instrument was set so that each nanogram represented one to two deflections of the photomultiplier scale.